Vulcanization of rubber with complex of monochloroborane and tertiary amine or triphenyl phosphine



Sept. 8, 1970 c. s. L. BAKER ETAL 3,527,744

VULCANIZA'IION OF RUBBER 'WITH COMPLEX OF MONOCHLOROBORANE AND TERTIARYAMINE OR TRIPHENYL PHOSPHINE I Filed May 9, 1968 g mcs 30//4oc. v \..230v E 210 k v;

BORON couczumnou (phr) CRISPN s-rum LEWIRNY muse.

DMJGLAS BARNMIB.

NQURJCE READ PDRTEl'mwm-ms Patented Sept. 8, 1970 U.S. Cl. 260-8058 6Claims ABSTRACT OF THE DISCLOSURE Chloroborane complexes are used asvulcanizing agents for natural rubbers and synthetic rubbers produced bysolution polymerisation, particularly cis-polyisoprene. When thevulcanizable mixture contains moisture, hydrogen evolution may beavoided by the addition of a drying agent such as calcium oxide. Theproducts show a high degree of resistance to attack by ozone making themuseful as coatings for conventional rubber articles.

This invention is concerned with the vulcanization of rubber, andrelates to vulcanizable compositions comprising natural or certainsynthetic rubbers, together with vulcanizing agents and other additives.

US. Pat. No. 2,558,559 teaches that boron hydrides are advantageousvulcanizing agents for two specific classes of synthetic rubbers,namely, certain co-polymers of butadienes and acrylonitriles, andpolymers of 2-chlorobutadiene-1,3, and states that boron hydrides alsohave some vulcanizing eflect on other rubbers, particularlybutadiene-styrene rubber and natural rubber. According to the UnitedStates patent, the boron hydride may be used in the form of a complexwith ammonia or with certain amines, or in the form of otherderivatives. When the uncomplexed boron hydride is used, it ispreferably added in admixture with an inert filler, for example,calcined clay, to reduce its infiammability.

We have found that, although boron hydride complexes are capable ofvulcanizing rubbers containing olefinic unsaturation, the process may behandicapped by the evolution of gas during cure, leading to porousvulcanizates.

It is thought that the gas, which has been shown to be mainly hydrogen,is primarily produced by reaction of the borane with small quantities ofwater present in many of the rubbers;

Bi; 3 W 3 JO.

where R is a second rubber chain.

A closely parallel elimination has been reported (H. C. Brown, K. J.Murray, H. Miiller and G. Zweifel, J. Am. Chem. Soc. 88, 1443 (1966)).

The present invention provides a vulcanizable composition comprisingnatural or an olefinically unsaturated synthetic rubber prepared bysolution polymerisation, a minor proportion of a chloroborane complex asa vulcanizing agent for the rubber, and optionally a drying agent. Adrying agent is desirable when the rubber contains substantial amountsof moisture.

It is believed that the replacement by a chlorine atom of one of thethree hydrogen atoms attached to boron prevents the internal eliminationreaction described above from taking place. Rubbers which containhydrogen atoms reactive in the above sense include natural and syntheticcis-polyisoprene, and the invention is particularly advantageous inrespect of such rubbers.

'Ihe vulcanizable composition should preferably not contain anysubstantial quantity of any non-rubber (other than water) which isreactive towards the chloroborane With or without gas evolution. Naturalrubber normally contains some acidic material, but the proportion may befound to be so small that no noticeable evolution of gas takes place onvulcanization. The synthetic rubber is one produced by solutionpolymerisation. Examples of synthetic rubbers which are produced by thismethod are: 1,4-polybutadiene, for example the high-cis product sold byPhillips Petroleum International Corporation under the trade name Cis-4;polyisoprene, for example, the high-cis product sold by Goodyear Tireand Rubber Company under the trade name Natsyn; styrene-butadieneco-polymers, for example, that sold by Phillips Petroleum InternationalCorporation under the trade name Solprene; and ethylene-propyleneterpolymers such as that sold by E. I. du Pont de Nemours and CompanyIncorporated under the trade name Nordel.

Synthetic rubbers produced by emulsion polymerisation do not normallygive attractive vulcanizates when chloroborane complexes are used, andgas evolution may be observed. Emulsion polymers normally contain asubstantial proportion, for example 5%, of fatty acids and soaps presentas surface-active agents, and it is believed that these react with thechloroborane complex to give hydrogen.

The term chloroborane complex is intended to include complexes ofmonochloroborane, BH Cl, with any complexing agent which does not itselfreact with the borane. The complexes may be readily formed, for examplewith amines, phosphines or phosphites. Examples aretn'methylamina-chloroborane (CH N:BH Cl, triethylamine-chloroborane (C HN:BH Cl, tri-ethylenediamine-bischloroboranetri-n-butylamine-chloroborane (C H N:BH Cl, andtriphenylphosphine-chloroborane (C H P:BH CL Complexes with sulphurandoxygen-containing compounds may be less stable.

The purpose of the complexing agent is to enable the chloroborane to behandled safely and conveniently at ambient temperatures. The nature ofthe complex influences the temperature at which vulcanization takesplace, so the choice of a suitable complexing agent may be dictated bythe desirability of performing vulcanization at temperatures above thoselikely to be reached when the components undergo the normal mixingprocesses.

The free amine is liberated from the complex during vulcanization.Volatile amines, such as trimethylamine, have unpleasant odours and maycause swelling of the vulcanizates. Complexes of the higher amines withbulky alkyl groups, such as tributylamine, tend to be too reactive andto cause premature vulcanization. The bischloroborane complex oftriethylenediamine has been found to be particularly suitable and hasthe added advantage of having a high boron content. Examples of othercomplexing agents will be apparent to those skilled in the art.Complexes of chloroboranes may be prepared by: (i) the method describedby J. E. Douglass in J. Org. Chem. 31, 962 (1966), except that in thecase of the tri- 20% C. below the minimum practical cure temperature.

Vulcanizates prepared according to this invention show unusualproperties in that they exhibit a high degree of stress relaxation and ahigh creep rate. It is thought that this is not due to insufiicientvulcanization, but rather ethylenediamine complex, N,N-dimethylformamideis 5 to the fact that a substantial proportion of the cross-links usedas solvent; or (ii) exchange reactions of the type are labile at roomtemperature. These properties find described by R. A. Baldwin and R. M.Washburn, J. Org. particular utility in one field. If the initialstrains are not Chem. 26, 3549 (1961), carrying out the exchange withtoo high, the ozone-resistance of these vulcanizates is simplechloroboranes prepared as in (i) above. very good, presumably becausethe high creep rate rap- The amount of the chloroborane complex requiredto idly brings the surface strain to below the critical level effectvulcanization may readily be determined by exat which cracking occurs.The invention therefore inperiment, depending on the nature of therubber, the ti eludes articles of natural or synthetic rubber which haveand temperature of cure, and the degree of crosslinking been providedwith an ozone-resistant coating or layer required. Suitable proportionsmay provide from 0.05% of a vulcanizate produced according to thepresent invento 0.5%, particularly from 0.2% to 0.4% by weight of ti0n.boron on t W ig t of the rubber to be "ulcalnilfidZ The followingexamples illustrate the invention. In the The y l agent, when P Shouldbe 0H6 Whlch tables, the following abbreviations have been used: reactschemlcally with moisture present in the rubber to give a product whichis substantially unreactive towards TEB: Triethylamine-borane thechloroborane. Conventional drying agents, such as TEDB:Triethylenediamine-bisborane synthetic zeolites, magnesium sulphate andcalcium sul- TPPB: Triphenylphosphine-borane phate hemihydrate, arerelatively ineffective because they TMCB: Trimethylamine-chloroboranehold the moisture only physically or as water of crystal- TECB:Triethylamine-chloroborane lisation. Phthalic anhydride is alsoineffective because, al- TEDCB: Triethylenediamine-bischloroboranethough it reacts with water, it gives a product, phthalic TPPCB:Triphenylphosphine-chloroborane acid, which itself reacts with thechloroborane. A pre- RSS1: Ribbed smoked sheets gradel ferred dryingagent is calcium oxide, either as such, or Heveacrumb SMR 5L: Trade namefor a technically in the form of a 75% w./w. dispersion in mineral oilas specified comminuted natural rubber sold by John and E. Sturge Ltd.,under the trade name HAP: High abrasion furnace of Caloxol C31. SRF:Semi-reinforcing furnace Enough of the drying agent should be present toreact Dutrex R: Trademark for an aromatlc 011 used as a procwith all themoisture (if any significant amount is pres- 635mg ald ent) in therubber. When the rubber contains moisture, PBN:phfnylbetanaphthylamlne'antloxldant an improvement is observed when 2phr. of drying agent PhT-Z Pans P hundred of rubber is present andproportions of from 4 to 10 phr. are adequate for use with all suchrubber mixes. It has been Table 1 detalls of vanous.types and t foundconvenient when a drying agent is required, to f cunng agent fillerdrying agent vanou? conuse 6 parts by weight of Caloxol C31 per 100 partb dltlons of cure, and some propertles of the vulcanlzates. weight ofrubber. Some synthetic rubbers do not contain 40 The amount of cunngagent glven m parts by Welght appreciable amounts of moisture, and adrying agent may of boron per Ri by Welght of the rubber2ln thetherefore not be required filler column, Yes means that parts by welghtof Conventional fillers, plasticisers, synthetic resins and E g g aadded perlloo ig B welght of other desired compounding ingredients maybe included t e w g F; z g co means that in conventional proportions inthe vulcanizable composi- 45 6 Parts y We1g.t o a 0X01 C3 have addelhpertions of this invention provided that they are inactive parts by Weightof the The curmg condltlons towards the chloroborane. g g d d 1 Theinvention also provides a method of vulcanizing z omposltlon Intro mou dprehealed' a natural or synthetic rubber, which method comprises 0 33 25; temperature ralsed to 1 0 total heatmg heating the vulcanizablecomposition hereinbefore de- 0 o fined for a time and at a temperatureto effect vulcanizag g l l heated for hour at 140 tion. Heating times offrom 10 minutes to 1 hour at tem- Omposmon mtrodpced Into mouldprehealed peratures of from 0 to 5 c. have been found to 110 C.temperature ralsed to 150 C., total heating convenient, but other timesand temperatures may be r lhour' a chosen. As no induction period isobserved when curing 50 (D) Composmon heated for 1 at with chloroboranecomplexes, it is preferred to intro- The relaxed at 100% extension 100)15 duce the vulcanizable composition into a mould which a stanflard testand is normally regankd as glvlng a has been preheated to a temperatureof not less than ful g f thc t f nlzatlon- TABLE 1 Rubber Curing AgentDrying MR 100 Example Type Wt. (g.) Typo Wt. (g.) B (phr Agent Cure(kg./cm.) Comments 25 TEDB 0.485 0. N0 A Badly blown. 25 'IEDB 0.485 0.4.0 Slightly blown. 40 TEB 1.28 0. 20.5 Do. 25 TEDB 0.4s5 0. 19.8 Do. 25TMCB 1.0 0. Sample blown. 60 TMCB 2.4 0. 6.6 Acccptable.* 40 TMCB 1.2 0.20.3 Do.* 25 TEDCB 0.725 0. 27.0 Satisfactory cure. 25 TEDCB 0.725 0.5.1 Do. 25 'IEDB 0.162 0. 6.0 Veryslightly blown. 25 'IEDB 0.162 0. 6.3Satisfactory cure. 25 TEDCB 0.212 0. 4.1 Slightly blown. 25 TEDCB 0. 2420. 5.1 Satisfactory cure. 25 TEDB 0.102 0. 6.0 Slightly blown. 5 SBRSolprcne- 25 TEDB 0.162 0. 0.0 Satisfactory euro. 10 SBB 1204 25 TEDCB0. 242 0. 1.5 Slightly blown.

See footnote at end of table.

TABLE 1--Continued Rubber Curing Agent Drying MR 100 Type Wt. (g) B(phr.) Filler Agent Cure (kg/em?) Comments TEDCB 0. 242 0. 1 5. 4Satisfactory cure. TEDCB 0.484 0.2 8.4 Do. TEDB 0. 324 0. 2 Sampleblown. TEDB 0. 324 0.2 4. 3 Satisfactory cure. TEDCB 0. 484 0. 2 4.0Non-uniform appearance. TEDB 0. 324 0. 2 Sample blown. TEDCB 0. 484 0. 25. 3 Do. TEDB 0.485 0.3 Do. TEDB 0.485 0.3 D0. TEDCB 0. 725 0. 3 3. 8satisfaetoly cure. TED CB 0. 725 0.3 5.1 Do. TPPB 1. 92 0.3 22. 8 Sampleblown. TIPPCB 1. 075 0. 3 32. 3 Satisfactory cure.

* Volatile amine liberated.

NOTE-Tensile strength N0. 3, 226 kg./cm. No. 6, 174 kgJcmfl; No. 7, 245kg./cm.

Of the first 29 examples, Nos. 5, 6, 7, 8, 9, 12, 13, 16, 17, 18, 21,26, 27 and 29 are within the scope of the present invention.vulcanizates which have blown slightly or have a non-uniform appearance,while not preferred, may be adequate for some purposes.

Examples 1 to 9 show that, as the natural rubber samples used containedmoisture, it was necessary to employ a drying agent. In the presence ofa drying agent, use of the chloroborane complexes prevents the formationof hydrogen, which occurs when the borane complexes are used. The use oftrimethylamine-chloroborane is not preferred, as the liberated aminecaused the sample to swell out of the mould and to have an unpleasantodour.

Internal hydrogen elimination during vulcanization is not a feature withcis-polybutadiene lubber (Examples 10-13), styrene-butadiene rubber(Examples 14-18), and ethylene-propylene terpolymer (Examples 19-21),and these rubbers can therefore be cured satisfactorily by both boraneand chloroborane complexes in the presence of drying agent whennecessary.

SBR Intol 1500 is an emulsion polymer and the vulcanizates from bothborane and chloroborane complexes were blown even in the presence ofdrying agent (Examples 22, 23). The synthetic cis-polyisoprene used inExamples 24 to 27 Was dry, but could only be satisfactorily cured bychloroborane complexes, due, presumably, to the internal hydrogenelimination mentioned above. Examples 28 and 29 relate to the use ofphosphine complexes of borane and chloroborane with natural rubber, andagain illustrate the advantage of a chloroborane complex.

In Examples 30 to 34, natural rubber (ribbed smoked sheets, grade 1) wasmixed with triethylenediaminebischloroborane (to provide 0.3 part byweight of boron per 100 parts by Weight of rubber) and 6 parts by weightof a drying agent per 100 parts by weight of rubber. Curing conditionsand comments on the vulcanizates are given below in Table 2.

TABLE 2 Ex. Rubber MR 100 N0. Wt. (g.) Drying Agent Cure (kg/cm?)Comments 30--.. 25 Molecular sieve D Badly type 4A. blown.

31.-.. 25 Freshly ignited D Slightly magnesium blown. sulphate.

32.... 25 Freshly ignited D 5.9 Satisfactory.

calcium oxide.

33.... 12.5 Calcium Sulphate A Badly hemihydrate. blown.

34--.- 12.5 Phthalic anhydride. A Do.

Molecular sieve type 4A is a synthetic zeolite particularly suited toabsorb water. The drying agent must react chemically with the moistureto produce a product which is unreactive towards the chloroborane.

Tables 3 and 4 set out certain preferred compositions and the initialproperties of vulcanizates prepared according to the invention fromthem. Proportions of ingredients are by weight.

TABLE 3.COMPOUNDING INGREDIENTS Example 35 36 37 38 39 40 41 RSS1 100100 100 100 100 100 Zinc oxide 5 5 5 5 TEDCB (0.3 phr. of boron). 2. 892. 89 2.89 TECB (0.2 phr. of boron) 2. 78 2. 78 2. 78 2. 78 Caloxol C316 6 6 6 6 6 6 Cure:

Time, minutes 30 30 30 40 35 40 40 Temp., C 150 150 150 100 110 100 100TABLE 4.INITIAL VULCANIZA'IE PROPERTIES Example Hardness BS) Relaxedmodulus, MR 100 (kg/cm?) Tensile strength (kg./cm. .lcmfi) Tearstrength, maximum (kg/mm.) at 21 C. Tear strength, maximum (kg/mm.) at CResilience (Lupke) (percent) Abrasion loss, average (Akron) (cc./500rev.) Flex life (do Mattia) (kc. to grade Cut growth (kc. to 8 mm.)Compression set (25%; 3d. at 21 C (percent Compression set (25%; 24 hr.at 70 0.) (percent Tension set of EB for 10 min.) (percent) 30 min.relaxation 1 Evidence of thermal degradation on reverse side of testpiece.

2 .2 mm. at 1,000.

Edge cracks at ends only; otherwise one isolated It will be seen thatthe vulcanizates in columns B and D, prepared using TEDCB and TECBrespectively, performed much better than the comparable vulcanizatesTABLE 5.--OZONE RESISTANCE Hours Exposure I I I I I I mmmmo e) o aONMMMMMMS IJI ONMWMCOMMB OONCOCOMMMS OOONMFQMCQ mmmm mmmm I I I INCOOOMMWNM Table 6 illustrates the ozone protection afforded to aconventional natural rubber vulcanizate by a thin skin of natural rubbercured by an amine-chloroborane.

A sheet, 0.4 mm. thick, of a TECB gum compound was applied to both sidesof a sheet of a CBS/S black stock, 1.2 mm. thick, and the laminate curedin a compression mould at 150 C. for 20 minutes. The chloroborane curedskin was perfectly bonded to the sulphur vulcanizate by this treatment.

Strips, 15 cm. by 1 cm., were cut from the laminated sheet, and from acontrol sulphur vulcanizate, strained to the extents indicated in Table6 and held at these strains for 76 hours before being placed in anatmosphere containing 25 p.p.h.m. of ozone. The edges of the strips werestrips were protected by a coating of a Hypalon lacquer. The grades ofcracking at various time intervals are defined as for Table 5.

Compounds TECB compound:

IRSSI ZnO 2O Caloxol 6 PBN 1 Boron 0.2 S/CBS stock:

RSSI 100 HAF black 50 Dutrex R 5 ZnO 5 Stearic acid 2 S 2.5 CBS 0.6

TABLE 6 Control, Unprotected S/CBS Black protected S/CBS Black by TECBgum skin Hours Exposure 24 48 54 96 168 24 48 54 96 168 Strain, percent:

Table 7 shows that no detrimental effect occurs with a TECB cure whenthe temperature and/or time of cure is increased (the tensile strengthand modulus remain virtually unaffected). The vulcanizable compositionfor Table 7 was as follows.

Compounding ingredients RSS1 100 HAF Black 50 TECB (0.2 phr. boron) 2.78Caloxol C31 6 PBN 1 TABLE 7 Cure Cure Tensile Elongation M 100 M 200 M300 temp. time strength at break EX. C (111111.) (kg./cm. (percent)(kg/cm!) The figure shows the variation of tensile strength with boronconcentration for natural rubber vulcanizates containing 50 phr. of HAPblack and cured with TMCB.

The vulcanized rubbers of the invention can be used for the samepurposes as prior known vulcanized rubbers,

9 e.g. in the manufacture in per se conventional manner of rubberarticles where resistance to creep is not a vital property.

We claim: 1. Vulcanizable rubber composition comprising (1) naturalrubber or an olefinically unsaturated rubber prepared by solutionpolymerization and selected from the group consisting of polybutadiene,polyisoprene, styrene-butadiene copolymers, and terpolymers fromethylene-propylene-diene monomers, and (2) a complex of monochloroboraneBH CI with tertiary amine or triphenyl phosphine, said complex beingpresent in an amount sufficient to provide from 0.05% to 0.5% by weightof boron based on the weight of the rubber to be vulcanized, with theproviso that the composition does not contain any appreciable quantityof any non-rubber other than water which is reactive towards thechloroborane with or without gas evolution. 2. A composition as claimedin claim .1, wherein calcium oxide is present as a drying agent.

3. A composition as claimed in claim 1 wherein the chloroborane is usedin the form of an amine complex. 4. A composition as claimed in claim 3,wherein the amine complex is triethylenediamine-bischloroborane ortriethylamine-chloroborane.

5. A composition as claimed in claim 1, wherein the proportion ofchloroborane complex present provides from 0.2% to 0.4% by weight ofboron on the weight of the rubber to be vulcanized.

6. A method of vulcanizing a natural or synthetic rubber, which methodcomprises heating the vulcanizable composition claimed in claim 1 for atime and at a temperature to effect vulcanization.

References Cited UNITED STATES PATENTS 2,558,559 6/1951 Hurd et a1260768 XR 3,225,017 12/1965 Seegman et al 26079.1

FOREIGN PATENTS 1,382,668 11/1964 France.

20 JOSEPH L. SCHOFER, Primary Examiner WILLIAM HAMROCK, AssistantExaminer US. Cl. X.R.

